Closed seas play very diverse roles in relations between their bordering states: they unite and separate, they are a place of transit, a shared space, an element of joint identity, a common heritage. This project focuses on four closed sea basins: those of the Mediterranean, Caspian, Baltic and Black seas. Those basins were theatres for strategic competition between the Soviet Union and the United States during the Cold War and acquired since 1989 a new centrality in co-operation amongst neighbouring states, with a wealth of sub-regional multilateral agreements and institutions flourishing in a few years. All four basins are crucial to the European Union, and the EU is at the same time a crucial actor in them. Its policies have an impact not only in each country, but also on collective efforts at sub-regional level. This is a seldom analysed phenomenon: that of the relationship between a uniquely successful international organisation with a nature of its own, the European Union, and the smaller sub-regional multilateral structures and agreements. Compared to the huge attraction that the EU exerts, which has been a catalyser for stability, change and reconciliation in a number of European countries, sub-regional multilateral institutions have proved their relative weakness. However, their role in a number of areas (from stability and conflict resolution, to environmental issues) has been and still is important. This project aims to evaluate their main achievements and failures, and the areas in which they have been most successful. At the same time, it aims to analyse how EU membership and EU policies impact on multilateral co-operation around the sea basins, and how the EU and other multilateral organisations and initiatives can co-operate in achieving their shared objectives. In the end, the project will explore what would be the benefits of a specific approach of the EU for each of the four basins, in co-operation with the existing sub-regional multilateralism.